Lean manufacturing is a production practice that considers the expenditure of resources for any goal other than the creation of value for the end customer to be wasteful, and thus a target for elimination. Working from the perspective of the customer who consumes a product or service, "value" is defined as any action or process that a customer would be willing to pay for. The goal of Lean is to becomes the creation and maintenance of a production system which runs repetitively, day after day, week after week in a manner identical to the previous time period. Lean is actually the set of "tools" that assist in the identification and steady elimination of waste. As waste is eliminated quality improves while production time and cost are reduced. Examples of such "tools" are Value Stream Mapping, 5S, Kanban (pull systems), and poka-yoke (error-proofing).
1.2Visual Stream Mapping (VSM)
Value stream mapping is a process designed to reduce lead time, to make product flow, and to eliminate waste (non value added operations or activities), all for the purpose of meeting customer demand at the lowest cost, and with the highest quality. Lean thinking relies on recognizing the “seven wastes” – over-production, over-processing, inventory, motion, scrap, waiting, and transportation. Target maps reveal which of these wastes can be eliminated now, and where. The key to producing useful target maps is to look for low-cost improvements that encourage flow, reduce inventory, and test the organization’s ability to manage in a lean environment. The challenge of developing the attitudes, systems and communication necessary for a true pull system operating at customer takt should not be underestimated. A high inventory system hides a multitude of problems, which will slowly be exposed as batch sizes and WIP are reduced. The level of organization and standardization required for one-piece flow are rarely found in companies with traditional production planning and traditional management. Visual Stream Mapping can identify wastes such as:
Over-production is the production of material which is not needed now. It usually occurs in the form of large batches, produced faster than the rate at which they can be consumed Over production is caused by a number of factors, such as long setups, poor quality, machine unreliability, avoidance of setups in order to make performance measures look better, or the desire to keep an expensive resource working.
There are two aspects to this kind of waste which is overdoing it in the sense of doing too much, too soon, and beyond what is necessary and using inappropriate equipment, especially equipment that is much larger, faster, or more complicated than necessary. It can be difficult to distinguish between over-processing and over-production, because the first often leads to the second. Over-processing is usually associated with going beyond what the customer requires. Examples are reports and presentations that have more information than the audience is looking for, and therefore are difficult to understand and act on.
Whether in the form of work in process (WIP) or finished goods, inventory is considered the great problem in production. With material always available, the focus is taken away from the process, quality, and the rate of work. Inventory thus actually hides problems that exist in the production system. In addition, inventory has an impact on waste that is indirectly caused by having more than needed. Inventory leads to a lack of attention to the process. This means that processes are designed with cycle times well outside of the average. By buffering the process with inventory, the wide variance in cycle times is not noticed until an attempt is made to set up a continuous flow cell or line.
When a facility layout extends over a large area, the movement of inventory...